296
OWE BERG, GAUKLER, AND SQUIER
the absence of dissolved hydrogen, i.e., after pickling it in 12N HNOs,
shows that the rate (Eq. 5) is small at all values of 6 and therefore
that the reaction does not occur within a period of 7 msec. The reaction of the second mechanism (Eq. 4) is found to occur within a period
of 0.2 msec.
The data disclose the interesting fact that hydrogen is much more
strongly hydrogen-replacing than is iron. This, of course, is well
known. They also suggest that iron free of hydrogen may not be hydrogen-replacing at all with respect to water. This point is difficult
to prove because as the period of observation is extended beyond 7
msec
traces of hydrogen become increasingly important until it is
very difficult to distinguish between the slow reaction of Eq. 3 and the
slow (H}small) reaction of Eq. 4.
Equation 6 expresses the rate of wetting by the second mechanism
(Eq. 4) because the OH,., is bonded to the water in the drop. On the
other hand, the reorientation rate, v, of bonds at the water surface is
v= k3V
(8)
When this rate is greater than the rate of Eq. 6, the formation of OH.a
contributes less to the wetting than does the mechanism of reorienta-
tion of bonds and bonding with already present OH,,,. Hence at high
voltages the rate should depend upon V. We may expect
v =k, [H,O] {H}, V small
(9)
and
v=k,V, V large
(10)
Such is not quite the case, however, because v is proportional to Vv’ at
high values of V. The samerelation is shown in the results with satu-
rated NaCl solutions in Figs. 7 to 10. Accordingly, the formula given
as Eq. 8 does not hold any more when
k3V > k, [H,O] {8}
|
(11)
In this region we have
v=k,v?
Hence, instead of Eqs. 7 and 8, we have
v =k, [H,O] {H}, V small
(12)